Disclosed in the embodiments herein is an improved, lower cost, system for sheet deskewing. Various types of automatic sheet deskewing systems are known in the art. The following previous patent disclosures are noted by way of examples. They demonstrate the long-standing efforts in this technology for more effective yet lower cost sheet deskewing, particularly for printers (including, but not limited to, xerographic copiers and printers). Also, they show that it is known to be desirable to have a sheet deskewing system that can be combined with a lateral sheet registration system, in the same or a modified apparatus. Also, to show that it is desirable for either or both sheet deskewing and lateral registration to be done while the sheets are moving along a paper path (xe2x80x9con the flyxe2x80x9d, without sheet stoppages). Especially for faster printing rates, requiring faster sheet feed rates, which can reach more than, for example, 100-200 pages per minute, the above systems and functions become even more difficult and expensive, as will be explained. However, it will be noted that the deskewing systems disclosed herein are not limited to just such high speed printing applications, nor limited only to combinations of sheet deskewing and sheet lateral (sideways) registration.
Disclosed in the embodiments herein is an improved system for controlling, correcting or changing the orientation and/or position of sheets traveling in a sheet transport path, in particular, sheets being printed in a reproduction apparatus, which may include sheets being fed to be printed, sheets being recirculated for second side (duplex) printing, and/or sheets being outputted to a stacker, finisher or other output or module.
Disclosed in the embodiments herein is a simple system for deskewing, and, optionally, also transversely repositioning, sheets with a simpler, lower cost, mechanism which needs only one single main drive motor for two feed roll drives, together with a much lower power, and lower cost, deskewing differential drive. This is in contrast to various of the below-cited and other systems which require two or even three separate, and separately controlled, servo or stepper motor drives. Yet the disclosed embodiments can provide active automatic variable sheet deskewing and optional, active variable side shifting for lateral registration, while the sheet is moving uninterruptedly at process speed. It is applicable to various reproduction systems herein generally referred to as printers, including high speed printers, and other sheet feeding applications. Furthermore, the deskewing system of the disclosed embodiments can provide reduced total mass, and therefor provide improvements in integral lateral registration systems involving rapid lateral movement thereof, such as the TELER type described below.
Various types of variable active sheet side shifting or lateral registration and/or deskew systems are known in the art. A recent example of this technology is Xerox Corp. U.S. Pat. No. 6,173,952 B1 issued Jan. 16, 2001 to Paul N. Richards, et al (and art cited therein). Furthermore, that patent""s disclosed additional feature of variable lateral nip spacing, for better control over variable size sheets, may be readily combined with or into various applications of the present invention, if desired.
As noted, it is particularly desirable to be able to do so xe2x80x9con the fly,xe2x80x9d while the sheet is moving through or out of the reproduction system at normal process (sheet transport) speed. Also, to be able to do so with a system that does not substantially increase the overall sheet path length, or increase paper jam tendencies. The following additional patent disclosures, and other patents cited therein, are noted by way of some examples of sheet lateral registration systems with various means for side-shifting or laterally repositioning the sheet: Xerox Corporation U.S. Pat. No. 5,794,176, issued Aug. 11, 1998 to W. Milillo; U.S. Pat. No. 5,678,159, issued Oct. 14, 1997 to Lloyd A. Williams, et al; U.S. Pat. No. 4,971,304, issued Nov. 20, 1990 to Lofthus; U.S. Pat. No. 5,156,391, issued Oct. 20, 1992 to G. Roller; U.S. Pat. No. 5,078,384, issued Jan. 7, 1992 to S. Moore; U.S. Pat. No. 5,094,442, issued Mar. 10, 1992 to D. Kamprath, et al; U.S. Pat. No. 5,219,159, issued Jun. 15, 1993 to M. Malachowski, et al; U.S. Pat. No. 5,169,140, issued Dec. 8, 1992 to S. Wenthe; and U.S. Pat. No. 5,697,608, issued Dec. 16, 1997 to V. Castelli, et al. Also, IBM U.S. Pat. No. 4,511,242, issued Apr. 16, 1985 to Ashbee, et al.
Various optical sheet lead edge and sheet side edge position detector sensors are known which may be utilized in such automatic sheet deskew and/or lateral registration systems. Various of these are disclosed the above-cited references and other references cited therein, or otherwise, such as the above-cited U.S. Pat. No. 5,678,159, issued Oct. 14, 1997 to Lloyd A. Williams, et al; and U.S. Pat. No. 5,697,608 to V. Castelli, et al.
Various of the above-cited and other patents show that it is well known to provide sheet deskewing systems, which may also provide lateral registration, in which a sheet is deskewed while moving through two laterally spaced apart sheet feed roller-idler nips, where the two separate sheet feed rollers are independently driven by two different respective drive motors. Temporarily driving the two motors at slightly different rotational speeds provides a slight difference in the total rotation or relative pitch position of each feed roller while the sheet is held in the two nips. That moves one side of the sheet ahead of the other to induce a skew (small partial rotation) in the sheet opposite from an initially detected sheet skew in the sheet as the sheet enters the deskewing system. Thereby deskewing the sheet so that the sheet is now oriented with (in line with) the paper path.
However, especially for high speed printing, sufficiently accurate continued process (downstream) sheet feeding requirements typically requires these two separate drive motors to be two relatively powerful and expensive servo-motors. Furthermore, although the two drive rollers are desirably axially aligned with one another to rotate in parallel planes and not induce sheet buckling or tearing by driving forward at different angles, the two drive rollers cannot both be fixed on the same common transverse drive shaft, since they must be independently driven.
For printing in general, the providing of either, and especially both, sheet skewing rotation or side shifting while the sheet is being fed forward in the printer sheet path is a technical challenge, especially as the sheet path feeding speed increases. Print sheets are typically flimsy paper or plastic imageable substrates of varying thinnesses, stiffnesses, frictions, surface coatings, sizes, masses and humidity conditions. Various of such print sheets are particularly susceptible to feeder slippage, wrinkling, or tearing when subject to excessive accelerations, decelerations, drag forces, path bending, etc.
The above-cited Xerox Corp. U.S. Pat. No. 4,971,304, issued Nov. 20, 1990 to Lofthus (and various subsequent patents citing that patent), is of interest as showing that a two nips differentially driven sheet deskewing system, as described above, can also desirably provide sheet lateral registration in the same unit and system, by differentially driving the two nips to provide full three axis sheet registration with the same two drive rollers and two drive motors, plus appropriate sensors and software. That type of deskewing system can provide sheet lateral registration by deskewing (differentially driving the two nips to remove any sensed initial sheet skew) and then deliberately inducing a fixed amount of sheet skew with further differential driving, and driving the sheet forward while so skewed, thereby feeding the sheet sideways as well as forwardly, and then removing that induced skew after providing the desired amount of sheet side-shift providing the desired lateral registration position of the sheet edge. This Lofthus-type lateral registration system may be optionally employed with the deskewing system herein as an alternative to the other lateral sheet registration systems disclosed herein.
In contrast to the above-described Lofthus ""304 system of sheet lateral registration with further controlled differential roll pair driving are sheet side-shifting systems in which the entire structure and mass of the carriage containing the two drive rollers, their opposing nip idlers, and the drive motors (unless splined drive telescopically connected), is axially side-shifted to side-shift the engaged sheet into lateral registration. These may be referred to as xe2x80x9cTELERxe2x80x9d systems, of, e.g., U.S. Pat. No. 5,094,442, issued Mar. 10, 1992 to Kamprath et al; U.S. Pat. No. 5,794,176 and U.S. Pat. No. 5,848,344 to Milillo, et al; U.S. Pat. No. 5,219,159, issued Jun. 15, 1993 to Malachowski and Kluger (citing numerous other patents); U.S. Pat. No. 5,337,133; and other above-cited patents.
For high speed sheet feeding, however, the rapid lateral acceleration of a large mass in such prior TELER systems requires yet another (third) large drive motor to accomplish in the brief time period in which the sheet is still held in (but passing rapidly through) the pair of drive nips. That is, the entire deskew mechanism of two independently driven transversely spaced feed roll nips must move laterally by a variable distance each time an incoming sheet is optically detected as needing lateral registration, by the amount of side-shift needed to bring that sheet into lateral registration. Also, an even more rapid opposite transverse return movement of the same large mass may be required in a prior TELER system to return the system back to its xe2x80x9chomexe2x80x9d or centered position before the (closely following) next sheet enters the two drive nips of the system. Especially if each sheet is entering the system laterally miss-registered in the same direction, as can easily occur, for example, if the input sheet stack side guides are not in accurate lateral alignment with the machines intended alignment path, which is typically determined by the image position of the image to be subsequently transferred to the sheets. Thus a TELER type system requires a fairly costly operating mechanism and drive system for integrating lateral registration into a deskew system.
To express this issue in other words, existing paper registration devices desirably register the paper in three degrees of freedom, i.e., process, lateral and skew. To do so in a single system or device, three independently controlled actuators are used in previous TELER type implementations in which the skew and process actuators are mounted on a carriage that is rapidly actuated laterally, requiring a relatively large additional motor. That is, the addition of lateral actuation requires the use of a laterally repositioning driven carriage, or a more complex coupling between lateral and skew systems must be provided. On the other hand, a Lofthus patent type system (as previously described) may require extra xe2x80x9cwigglingxe2x80x9d of the sheet by the drive nips to add and remove the induced skew, and that extra differential sheet driving (driving speed changes) can have increased drive slip potential. In any of these systems, or the xe2x80x9cSNIPSxe2x80x9d system noted below, the use of sheet position sensors, such as a CCD multi-element linear strip array sensor, could be used in a feedback loop for slip compensation to insure the sheet achieving the desired three-axis registration. See, e.g., the above-cited U.S. Pat. No. 5,678,159 to Lloyd A. Williams, et al.
Other art of lesser background interest on both deskewing and side registration, using a pivoting sheet feed nip, includes Xerox Corp. U.S. Pat. Nos. 4,919,318 and 4,936,527, issued to Lam Wong. However, as with some other art cited above, these Wong systems use fixed lateral sheet edge guides against which the side edges of all the sheets must rub as they move in the process direction, with potential wear problems. Particularly noted as to a pivoting nips deskew and side registration system without such fixed edge guides is the xe2x80x9cSNIPSxe2x80x9d system of both pivoting and rotating plural sheet feeding balls (with dual, different axis, drives per ball) of Xerox Corp. U.S. Pat. No. 6,059,284, issued May 9, 2000 to Barry M. Wolf, et al. However, the embodiments disclosed herein do not require such pivoting (dual axis) sheet engaging nips. I.e., they do not require pivoting or rotation of sheet drive rollers or balls about an additional axis or rotation orthogonal to the normal concentric drive axis of rotation of the sheet drive rollers. Also, the disclosed embodiments allow the use of normal low sheet slippage high friction feed rollers which may provide normal roller-width sheet line engagement in the sheet feeding nips with an opposing idler roller, rather than ball drives with point contact as in said U.S. Pat. No. 6,059,284.
As noted above, and as further described for example in the above-cited U.S. Pat. No. 6,173,952 B1 and other art cited therein or above, existing modern high speed paper registration devices more typically use two spaced apart sheet drive nips to move the paper in the process direction, with the velocities of the two nips independently driven and controlled by each having its own relatively expensive servo drive motor. Paper skew may thus be corrected by prescribing different velocities (V1, V2) for the two nips (nip 1 and nip 2) with the two servo-motors for a defined short period of time while the sheet is in the two nips. Typically, rotary encoders measure the driven angular velocity of both nips and a motor controller or controllers keeps this velocity at a prescribed target value V1 for nip 1 and V2 for nip 2. That velocity may be maintained the same until, and during, skew correction. The skew of the incoming paper is typically detected and determined from the difference in the time of arrival of the sheet lead edge at two laterally spaced sensors upstream of the two drive nips, multiplied by the known incoming sheet velocity. That measured paper skew may then be corrected by prescribing, with the motor controller(s), slightly different velocities (V1, V2) for the two nips for a short period of time while the sheet is in the nips. Although the power required for that small angular speed differential V1, V2 change (a slight acceleration and/or deceleration) for skew correction is small, both servo-motors must have sufficient power to continue to propel the paper in the forward direction at the proper process speed. That is, for this deskewing action, nip 1 and nip 2 are driven at different rotational velocities. However, the average forward velocity of the driven sheet of paper is 0.5 (V1+V2) and that forward velocity is desirably maintained substantially at the normal machine process (paper path) velocity. Two degrees of freedom (skew and forward velocity) are thus controlled with two independent and relatively large servo-motors driving the two spaced nips at different speeds in these prior systems.
Although the drive systems illustrated in the examples herein are shown in a direct drive configuration, that is not required. For example, a timing belt or gear drive with a 4:1 or 3:1 ratio could be alternatively used.
As noted above, providing the remaining lateral or third degree of sheet movement freedom and registration in present systems which desirably combine deskew and lateral registration may require control by a third large servo-motor, as in TELER type lateral registration systems described above, and relatively complex coupling mechanisms, for a further cost increase.
In any case, even in the above-described deskewing systems per se, since the two sheet driving and deskewing nips are completely independently driven, both drive motors therefor must have sufficient power and variable speed control to accurately propel the paper in the forward (process or downstream) sheet feeding direction at the desired process speed.
In contrast, the embodiments herein disclose a sheet deskewing system that needs only one (not two) such forward drive motor, for both nips, with sufficient power to propel the paper in the forward direction, and a second smaller and cheaper motor and differential system. That is, showing how to use only one drive to propel the paper in the forward direction and a second and much smaller and cheaper skew correction drive to correct for skew through a differential mechanism adjusting the rotational phase between the two nips without imposing any of the sheet driving load on that skew correction drive. This can provide a significant cost savings.
In other words, especially in high productivity machines, where the sheet feeding forward velocity is substantial, that requirement has heretofore imposed the selection and use of at least two high performance motors/controllers for such sheet deskewing systems, at substantial cost. In contrast, the disclosed embodiments enable a single drive motor to positively drive both spaced apart sheet drive nips of the deskewing system yet enable a low cost actuator to provide similarly effective paper deskewing by providing a similar deskewing speed differential between those same two driven nips, thereby substantially reducing the overall cost of the deskewing system. More specifically, teaching herein how to use one motor for the power needed to move the paper in the forward (process) direction with both nips and a second and much smaller motor to correct for skew through a differential mechanism adjusting the phase between those two otherwise commonly driven drive nips.
A specific feature of the specific embodiments disclosed herein is to provide a sheet skewing and sheet forward feeding system for inducing skew rotation of a sheet while also feeding the sheet forwardly in a sheet path with first and second laterally spaced positively driven sheet feeding nips, wherein said sheet skewing system selectably provides a difference in said driving of said first and second positively driven sheet feeding nips for said inducing of said rotation of a sheet, the improvement comprising a differential drive system for said inducing of said skew rotation of the sheet said differential drive system operatively connecting between said first and second laterally spaced sheet feeding nips, a differential drive motor controlling said differential drive system, and a single forward drive motor operatively connected to positively drive both of said first and second laterally spaced positively driven sheet feeding nips to feed the sheet forwardly in the sheet path by said single forward drive motor being operatively connected to at least one of said first and second laterally spaced positively driven sheet feeding nips through said differential drive system, said differential drive motor being of substantially lower power than said forward drive motor.
Further specific features disclosed in the embodiments herein, individually or in combination, include those wherein said sheet path is the sheet path of a printer and said sheets are flimsy imageable print substrate sheets being automatically deskewed in said sheet skewing and sheet forward feeding system, and/or said differential drive system comprises a laterally movable variable angle mechanical interconnection between said first and second laterally spaced positively driven sheet feeding nips, and/or said differential drive system comprises a laterally movable variable angle mechanical interconnection between said first and second laterally spaced positively driven sheet feeding nips which is laterally driven by said differential drive motor, and said differential drive motor is a much smaller motor than said forward drive motor, and/or said differential drive system comprises a laterally movable variable angle mechanical interconnection between said first and second laterally spaced positively driven sheet feeding nips, wherein said variable angle is provided by at least one laterally variable helical interconnection, and/or said differential drive system comprises a laterally movable variable angle mechanical interconnection between said first and second laterally spaced positively driven sheet feeding nips, wherein said variable angle is provided by a laterally movable interconnect sleeve with a helical pin-riding slot driven by said differential drive motor, and/or said forward drive motor is directly drivingly connected to only one of said first and second laterally spaced positively driven sheet feeding nips, and/or said forward drive motor is directly drivingly connected to one of said first and second laterally spaced positively driven sheet feeding nips through a drive system allowing lateral movement of said first and second laterally spaced positively driven sheet feeding nips relative to said forward drive motor, and said forward drive motor is mounted in a fixed position, and/or said differential drive system is automatically centered by said differential drive motor when the sheet is not in said first and second laterally spaced positively driven sheet feeding nips, and/or a controlled angular difference between said plural laterally spaced apart sheet drivers provides said sheet deskewing, the improvement comprising driving said plural laterally spaced apart sheet drivers with a single drive motor and also providing said controlled angular difference between said sheet drivers by a differential system connection between said sheet drivers, and/or said differential system is driven by a differential motor of much lower power and size than said single drive motor, and/or said differential system connection comprises a laterally movable variable angle mechanical interconnection between said plural laterally spaced apart sheet drivers, and/or said differential system connection comprises a laterally movable variable angle mechanical interconnection between said plural laterally spaced apart sheet drivers, which laterally movable variable angle mechanical interconnection is laterally driven by a much smaller motor than said single drive motor, and/or said differential system connection comprises a laterally movable for helical movement mechanical interconnection between said plural laterally spaced apart sheet drivers, which is laterally movable by a much smaller motor than said single drive motor, and/or only one of said plural laterally spaced apart sheet drivers is directly driven by said single drive motor, and/or said plural laterally spaced apart sheet drivers are laterally movable relative to said single drive motor, and/or said differential drive system is automatically centered by said differential drive motor when the sheet is not in said plural laterally spaced apart sheet drivers, and/or said plural laterally spaced apart sheet drivers are a single laterally spaced pair of sheet driving nips.
The disclosed system may be operated and controlled by appropriate operation of conventional control systems. It is well known and preferable to program and execute imaging, printing, paper handling, and other control functions and logic with software instructions for conventional or general purpose microprocessors, as taught by numerous prior patents and commercial products. Such programming or software may of course vary depending on the particular functions, software type, and microprocessor or other computer system utilized, but will be available to, or readily programmable without undue experimentation from, functional descriptions, such as those provided herein, and/or prior knowledge of functions which are conventional, together with general knowledge in the software or computer arts. Alternatively, the disclosed control system or method may be implemented partially or fully in hardware, using standard logic circuits or single chip VLSI designs.
The term xe2x80x9creproduction apparatusxe2x80x9d or xe2x80x9cprinterxe2x80x9d as used herein broadly encompasses various printers, copiers or multifunction machines or systems, xerographic or otherwise, unless otherwise defined in a claim. The term xe2x80x9csheetxe2x80x9d herein refers to a usually flimsy physical sheet of paper, plastic, or other suitable physical substrate for images, whether precut or web fed. A xe2x80x9ccopy sheetxe2x80x9d may be abbreviated as a xe2x80x9ccopyxe2x80x9d or called a xe2x80x9chardcopy.xe2x80x9d A xe2x80x9csimplexxe2x80x9d document or copy sheet is one having its image and any page number on only one side or face of the sheet, whereas a xe2x80x9cduplexxe2x80x9d document or copy sheet has xe2x80x9cpagesxe2x80x9d, and normally images, on both sides, i.e., each duplex sheet is considered to have two opposing sides or xe2x80x9cpagesxe2x80x9d even though no physical page number may be present.
As to specific components of the subject apparatus or methods, or alternatives therefor, it will be appreciated that, as is normally the case, some such components are known per se in other apparatus or applications which may be additionally or alternatively used herein, including those from art cited herein. All references cited in this specification, and their references, are incorporated by reference herein where appropriate for teachings of additional or alternative details, features, and/or technical background. What is well known to those skilled in the art need not be described herein.